A seal between the bottom part of the water compartment and the tubes in heat exchangers poses particular difficulties, especially in "solderless" heat exchangers, in which the tubes are not soldered to the water compartment while thin bottoms must be used.
It is known to expand the tubes conically after asssembly with the water compartment bottom by an appropriate punch in order thereby to produce a firm seat in the water compartment bottom. It is also known to provide the water compartment bottom in the immediate vicinity of each tube with an annular flange, a "passage," which grips the tube for a certain portion of its length. In known heat exchangers of this type, sealing elements are also provided between the passage and the tube.